1. Field of the Invention
The invention relates to a planar antenna in general and, more specifically, to a planar antenna with a directional pattern adjustable by means of an adjustment feed by way of a passive network.
2. Description of the Background Art
Microstrip beam antennas are well known in the art and present a number of disadvantages, e.g. narrow bandwidth and low efficiency, in addition to their essential advantages which result from desirable dimensions, simplicity of manufacture, and compatibility with printed circuits. In many respects, the manufacturing technology employed in microstrip antennas has not met established environmental specifications, which has resulted in these antennas being used only to a limited extent.
EP-A-O 253,128 describes a planar suspended conductor antenna array comprising tiered substrates between a pair of conducting plates. Each plate has openings spaced at intervals that define radiation elements. At least one exciter probe on a substrate has a plurality of openings. The signals received with these exciter probes are input to a suspended conductor in phase by means of conducting films. Holders for the substrate are mounted around the openings. The substrate is accordingly evenly supported and cannot warp. There are a number of wide grooves in the printed circuit boards between each row of adjacent openings, in which a plurality of suspended conductors are tip-stretched parallel to each other.
Antennas of this type are provided for high-frequency satellite transmissions. Because of the simplicity of the design, manufacturing costs can be lowered while high performance characteristics are achieved.
With an antenna having the above-described structure, the radiation pattern is exclusively in the form of a beam, such as is known, for example, from radar engineering.
A similar method is discussed in an article in Electromagnetics, Vol. 9, 1989, pages 385-393. This article describes a further development which is an antenna designed as a strip-slot-foam-inverted patch (SSFIP) antenna.
This SSFIP antenna is formed having tiered layer structure. Specifically, the SSFIP comprises a microstrip (S strip) with a quarter-wave stub, a slotted base, a foam layer characterized by slight attenuation and low relative permittivity, and lastly, an inverted radiating element in the form of a patch printed on a cover (inverted patch). One advantage of an antenna of this type is represented by simplicity in achieving circular polarization, and the possibility of operating two polarizations simultaneously.
In this design, the foam layer prevents surface wave propagation and increases the bandwidth.
There are several problems associated with the known SSFIP antennas described above. For example, there is a need for these antennas to be assembled with simpler and less expensive materials. Also, these known antennas have not been amenable to tailoring the radiation to specific needs.
The present invention is directed to overcoming the problems associated with the prior art antennas as will become apparent from the features described and claimed as follows.